Adam J. R. Kent

Oregon State University | OSU · College of Earth, Ocean and Atmospheric Sciences

Monogenetic basaltic cinder cones are abundant on Earth and exhibit a wide range of eruptive styles, including violent explosions. However, the mechanisms driving explosive cinder cone eruptions are still poorly understood. Here we investigate relations between volatiles, degassing, and crystallization in a long-lived, historical, cinder cone erupt...

Four Indian Ocean deep-sea tephras can be correlated to individual Oligocene on-land silicic pyroclastic units found in the Afro-Arabian flood volcanic province (Yemen and Ethiopia), providing valuable stratigraphic marker horizons. They also preserve among the largest geochemical heterogeneities observed in individual eruption events (SiO2: 43 to...

We present new compositional data on a suite of historic lava flows from the Reykjanes Peninsula, Iceland. They were erupted over a short time period between c. 940 and c. 1340ad and provide a snap-shot view of melt generation and evolution processes beneath this onshore, 65km long, ridge segment. The lavas are tholeiitic basalts (MgO 6.5–9.2wt%) a...

We report the results of in-situ laser ablation ICP–MS analyses of anorthite content, trace-element (Li, Ti, Sr, Ba, La, Pr, Ce, Nd, Eu, Pb) concentrations, and Pb-isotope compositions in plagioclase from eight dome-dacite samples collected from the 2004–5 eruption of Mount St. Helens and, for comparison, from three dome samples from 1981–85. For 2...

Petrologic studies of volcanic ash are commonly used to identify juvenile volcanic material and observe changes in the composition and style of volcanic eruptions. During the 2004-5 eruption of Mount St. Helens, recognition of the juvenile component in ash produced by early phreatic explosions was complicated by the presence of a substantial propor...

Oxidation of the subarc mantle in subduction zones can greatly affect mineral phase equilibria, the speciation of volatiles, and the transfer of multivalent elements in basaltic magmas. While peridotite xenoliths provide the most direct approach to measuring mantle oxidation states, such xenoliths in continental arcs are rare. In this investigation...

Previous studies have demonstrated that chemical analysis of relict primary igneous clinopyroxene crystals from komatiite lavas provide a means to investigate pre-metamorphic magmatic compositions and to assess similarities between komatiites and mafic magmas from modern plume or subduction zone environments. For this study we have analyzed major a...

Compositional variability of back-arc magmas may be attributed in part to differing amounts of added slab component. Such variability would presumably correlate with distance to the magmatic front and height above the subducting slab. However, compositions of glasses and melt inclusions sampled from the southern Mariana Trough back-arc (13.3° - 14°...

Snow Peak is a voluminous (>150 km3), glacially dissected shield volcano located approximately 50 km southeast of Salem, OR, with a summit height of 1,310 m above sea level. Snow Peak lies approximately 60 km west of the current High Cascade arc axis. Lavas from the southeast face of Snow Peak have been previously dated using K-Ar at ~3 Ma. New Ar-...

Hydrothermal ore deposits associated with arc magmatism represent important sulfur anomalies. During degassing of magmatic systems the volatile may transport metals and sulfur and produce deposits. The ultimate origin of the magma-derived sulfur is still uncertain. The Yanacocha high-sulfidation epithermal Au deposit, Peru, is hosted by a Miocene v...

We measured 210Pb-222Rn-226Ra disequilibria in samples representing a time sequence through the June 15, 1991 cataclysmic eruption tephras of Mount Pinatubo volcano, Philippines. Previous U- series degassing studies have interpreted 210Pb excess to indicate rapid volatile transport (differential 222Rn motion) and subsequent volatile accumulation. M...

An investigation of the Pb isotopic compositions of plagioclase and sulfide in a stratigraphic interval including the UG2 chromitite of the eastern Bushveld Complex has been conducted to determine the Pb isotopic composition(s) of the magma(s) that crystallized to form this part of the intrusion, gain a better understanding of why coexisting plagio...

We present trace element and Sr-Nd-Hf-Pb isotope compositions for clinopyroxenes from anhydrous spinel peridotite and garnet ± spinel pyroxenite xenoliths of Pan-African lithospheric mantle from Jordan, including the first high-precision double-spike Pb isotope measurements of mantle clinopyroxene. Clinopyroxenes from the peridotites are variably T...

Volcanic gases are intimately related to degassing and their study allows the characterization of the composition, concentration and origins of volatiles in magma. Exsolution and loss of volatiles, particularly H2O, CO2 and S, leads to major changes in magma crystal content, density and viscosity, which in turn can produce major shifts in eruption...

Dome lavas from the 2004 eruption of Mount St. Helens show elevated Li contents in plagioclase phenocrysts at the onset of dome growth in October 2004. These cannot be explained by variations in plagioclase-melt partitioning, but require elevated Li contents in coexisting melt, a fact confirmed by measurements of Li contents as high as 207 mug/g in...

In order to better understand what controls sulfur speciation in melt inclusions, and how that pertains to the original basalt composition, we have conducted a series of heating experiments on naturally quenched and crystalline olivine-hosted melt inclusions. Sulfur speciation was determined from S Kα peak shift measurements by electron microprobe...

Submarine lavas from Pitcairn and the Society Islands offer a unique opportunity to investigate volatile contents in melts derived from mantle OIB sources, and in particular to constrain the composition and origin of the EM-1 and EM-2 mantle endmembers. We present here the results of a study on volatile abundances in dredged glasses from Pitcairn a...

Anorthitic, AN greater than 90, plagioclase-phyric pillow basalts have been recovered from almost every Mid Ocean Ridge (MOR). These phenocrysts typically contain bands of primitive (high MgO) melt inclusions (MI's). Previous workers have described large variations in the abundance of Ti in melt inclusions within a single anorthite crystal. The ori...

In-situ analysis of Li and other trace elements in plagioclase and melt inclusions from the October 2004 eruption of Mount St Helens, Washington show a distinct enrichment in Li in plagioclase in lavas and ashes erupted during the initial phase of the eruption. Li contents are up to ~40 mug/g in plagioclase phenocrysts from ash and dome material fr...

Lithium and Cu should preferentially partition into volatile phases such as brines relative to silicate melts, and as such, fluctuations of these elements in phenocrysts, recorded through crystallization or diffusion, may provide a means to track changes in the volatile concentration and composition of a magma. Two examples focusing on feldspar and...

We have studied the relationship between lava composition and magma chamber processes at Mount Hood, Oregon for the last 475,000 years. Mount Hood is unusual, in comparison to nearby Mount St. Helens and Mount Jefferson, in that it has produced relatively homogeneous lava compositions over this time period. Erupted lavas are mostly crystal rich and...

The late Eocene to early Oligocene intrusions in the central Coast Range of Oregon, are a unique example of forearc magmatism. Characterized by an unusual chemistry for a subduction zone setting, the Oregon Coast Range Intrusions (OCRI) are not well understood and have undergone little investigation in recent decades. OCRI magmatism may have result...

Unusually magnesian (Mg# ∼76) basalts have been sampled from a small submarine volcano situated on the Mariana arc magmatic front. Total alkalis range from 1.7 to 1.94%, Al2O3 from 9.09 to 10.3% and CaO from 13.9 to 14.09%. These lavas can be classified based on mineralogy as picrite and ankaramite. Olivine-hosted melt inclusions (MIs) have median...

We report techniques for in-situ abundance measurements of the light-lithophile elements (LLE; Li, Be, and B) in silicate glasses by laser-ablation inductively coupled mass spectrometry (LA-ICP-MS), and compare the analytical performance of a sector field and quadrupole mass analyzer for these measurements. LA-ICP-MS is shown to be an effective mea...

Igneous rock textures vary markedly. They are the product of a wide range of processes, such as magma mixing-mingling, crystallisation, crystal recycling, nucleation events, textural equilibration, etc. The study and quantification of textures provides a direct measurement of the end product of these processes and thus provides a window into the jo...

[1] We present new analytical data of major and trace elements for the geological MPI-DING glasses KL2-G, ML3B-G, StHs6/80-G, GOR128-G, GOR132-G, BM90/21-G, T1-G, and ATHO-G. Different analytical methods were used to obtain a large spectrum of major and trace element data, in particular, EPMA, SIMS, LA-ICPMS, and isotope dilution by TIMS and ICPMS....

Oligocene Afro-Arabian bimodal flood volcanism produced a series of voluminous silicic pyroclastic eruptions (60 to >3000 km3 dense rock equivalent, ca. 29.5 Ma) that are geochemically and magnetostratigraphically correlated to four deep-sea Indian Ocean ash layers located ~2700 km to the SE. In excess of 1300 major element analyses on over 1050 sh...

Evaluating the potential role of crustal assimilation in modifying the compositions of flood basalt magmas is critical if we are to better understand the ultimate mantle origins and tectonic driving forces behind these immense episodes of melting. This question is particularly important for flood basalts such as the Early Cretaceous Paraná-Etendeka...

Relatively little is known about the abundances of volatile elements (H, C, Cl, S) in komatiite magmas, although this information provides potentially important constraints on the volatile content, evolution and outgassing of the Archaean mantle. One means to obtain this information is via studies of melt inclusions in komatiites and other olivine-...

Determination of sulfur speciation, based on the S Kalpha peak shift, by electron microprobe analysis has been well documented for glasses, however analysis of S speciation in melt inclusions provides additional complications. Apart from issues related to smaller sample sizes, rehomogenization of melt inclusions prior to analysis also has the poten...

Production rates of molecular oxides (M16O+/M+) of Ba and light rare earth elements (LREE: La, Ce, Pr and Nd), have been measured by Laser Ablation ICP-MS (LA-ICP-MS) analysis via ablation of a Ba and LREE-doped synthetic silicate glass. Our work confirms that oxide production is related to the strength of the M–O bond in the MO+ ion, and in agreem...

ABSTRACT,erties, and thus leads to questions about the uncon- ditional use of Darcy’s Law for multiphase,flow prob- Pore-scale multiphase flow experiments were developed to nonde- lems.Mortensenandcoworkersusedaquantitativelight structively visualize water flow in a sample of porous material using X-ray microtomography. The samples were exposed to...

Oxidation states of primitive, subaerially-erupted basalts, in the Oregon segment of the Cascade volcanic arc, have been determined by S Kalpha peak shift measurements and olivine-spinel oxygen barometry. Olivine-hosted melt inclusions, with sulfur concentrations ranging from 0.080 to 0.503 wt.% S, have oxidation states varying from -0.8 to +1.8 lo...

We will present trace element concentrations, measured by laser ablation ICP-MS, in eruptive material from the 2004 eruption of Mt St Helens, Washington. This material includes ash entrained in convecting steam plumes and material from the actively growing lava dome. Among other things this data will allow us to compare: (a) the trace element compo...

Chlorine is an excellent tracer of contributions of slab-derived fluids to mantle-derived melts produced during subduction zone magmatism, as saline fluids released during slab dehydration are enriched in chlorine by several orders of magnitude over mantle peridotite. Chlorine and other halogens also strongly influence the solubility of many cation...

Nous présentons les données de concentration de onze Terres Rares (La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Er, Yb, Lu) dans onze matériaux géochimiques de référence internationale obtenues par dilution isotopique et analyse par spectrométrie à source à plasma induit et multicollection (MC-ICP-MS). Nous avons analysé ces échantillons à la fois sous forme de...

Olivine- and feldspar- hosted melt inclusions (MI) in lavas dredged from the cross-chain along 14° 35' N in the southern Mariana arc provide a unique means of examining the cross-arc variability of outputs from the Subduction Factory. Unlike in the shorter Guguan cross-chain near 17° 20'N (Stern et al. this session), in the 14° 35'N cross-chain lav...

Newberry Volcano, located 60 km east of the central Oregon High Cascades resides in a complex tectonic and volcanic region. Understanding the petrogenesis of Newberry Volcano is important to understanding the regional geological framework because of its location at the confluence of the back-arc of the Oregon Cascades, the northern end of the Basin...

This experimental study examines the mineral/melt partitioning of incompatible trace elements among high-Ca clinopyroxene, garnet, and hydrous silicate melt at upper mantle pressure and temperature conditions. Experiments were performed at pressures of 1.2 and 1.6GPa and temperatures of 1,185 to 1,370C. Experimentally produced silicate melts contai...

We present the results of melting experiments on a moderately depleted peridotite composition (DMM1) at 10 kbar and 1250–1390°C. Specially designed experiments demonstrate that liquids extracted into aggregates of vitreous carbon spheres maintained chemical contact with the bulk charge down to melt fractions of ∼0·02–0·04 and approached equilibrium...

Widespread silicic pyroclastic eruptions of the Oligocene Afro-Arabian flood volcanic province (ignimbrites and airfall tuffs) produced up to 20% of the total flood volcanic stratigraphy (>6×104 km3). Volumes of individual ignimbrites and tuffs exposed on land range from ∼150 to >2000 km3 and eight major units (15–100 m thick) were erupted in <2 My...

We present elemental and isotopic (Sr-Nd-Pb-Hf-Os-He) data on primitive alkalic lavas from the Prinsen af Wales Bjeige, East Greenland. Stratigraphical, compositional and Ar-40-Ar-39 data indicate that this inland alkalic activity was contemporaneous with the upper parts of the main tholeiitic plateau basalts and also postdated them. The alkalic ro...

Studies of melt inclusions from basaltic lavas are often aimed at elucidating the nature of mantle source(s) and/or the processes responsible for melt generation. However, melt inclusions also provide unique insights into the architecture of basaltic magma systems, and melt inclusion compositions can potentially constrain the nature, timing, locati...

Binary mixing between compositionally distinct melts has been recognised as an important process in generating the compositional diversity of oceanic magmatism at several length scales, and it has been argued that local variations in 238U-230Th of MORB lavas are controlled by such a process. Additional information about the melting behaviour of the...

Our current understanding of groundwater flow and contaminant transport in the subsurface is, to a large degree, limited by existing measurement techniques. To correctly describe transport of contaminant species, it is essential to understand the interplay of advection, mechanical dispersion, and diffusion and their dependency on soil water distrib...

Measurements of chlorine concentrations in matrix glasses from 18 primitive (>6 wt% MgO) and eight evolved lavas from active spreading centers in the Lau Basin back-arc system provide insight into the processes which control chlorine concentrations in subduction-related magmas, and can be used to investigate chlorine enrichment related to fluids de...

Melt inclusions from Oligocene continental flood basalts (CFB) erupted in Yemen provide unique insight into the timing and nature of the processes that lead to crustal contamination and melt aggregation in CFB magmas. Large variations in trace element indices that are sensitive to the degree and composition of assimilated crustal material (e.g. K2O...

We will present the initial results of a comprehensive study of a suite of historic lava flows from the Reykjanes Peninsula (SW Iceland), a region that represents the onshore continuation of the oceanic Reykjanes Ridge spreading centre. These lavas were erupted over a relatively short time period between 874 AD and 1325 AD and thus provide a snap-s...

We have measured the major and trace element compositions of a suite of olivine-hosted melt inclusions in basaltic lavas from the islands of Agrigan and Guguan (one sample each) from the Mariana arc, part of the larger Izu–Bonin–Mariana system. The two lava samples examined show distinctly different chemical signatures that are considered to repres...

Cl is a potentially powerful tracer of saline slab-derived fluids in subduction zones. Salinity also controls the solubility of many other chemical species, and thus Cl contents are important for mass transfer considerations. Direct examination of the Cl contents of primitive arc magmas has been limited by a lack of suitable undegassed samples, how...

We have measured the rates of chemical diffusion of Mg in calcite and Ca in magnesite and used these new data to constrain the formation temperature and thermal history of carbonates in the Martian meteorite ALH84001. Our data have been collected at lower temperatures than in previous studies and provide improved constraints on carbonate formation...

The Olary Domain, part of the Curnamona Province, a major Proterozoic terrane located within eastern South Australia and western New South Wales, Australia, is an excellent example of geological region that has been significantly altered by metasomatic mass-transfer processes associated with regional metamorphism. Examples of metasomatically altere...

Many tholeiitic and transitional pillow-rim and fragmental glasses from Loihi seamount, Hawaii, have high Cl contents and Cl/K2O ratios (and ratios of Cl to other incompatible components, such as P2O5, H2O, etc.) relative to other Hawaiian subaerial volcanoes (e.g., Mauna Loa, Mauna Kea, and Kilauea). We suggest that this results from widespread co...

We report major element, H2O, Cl, B, and Be analyses of matrix glass and olivine-hosted glass inclusions from two pillow lava samples dredged from 4200 m on the southern rift zone of Loihi seamount, Hawaii. Matrix glasses (MgO∼9 wt.%) have H2O, Cl, and B contents considerably in excess of the values expected from mantle melting or fractional crysta...

This paper reviews the application of radiogenic isotopes to the study of four Cu‐U and Au deposits or deposit types in the Australasian region: Olympic Dam, Porgera, the Proterozoic Au deposits of the Tennant Creek district and the Archaean gold deposits of the Yilgarn Craton. In each case it has been possible to date the mineralisation and to cor...

Homblende and biotite that formed during gold mineralisation at the Scotia mine, Western Australia, have erratic 40Ar39Ar release spectra and total gas ages that are ∼200–900 million year younger than the ca. 2600–2620 Ma minimum age of gold mineralisation, as given by 40Ar39Ar plateau (muscovite) ages of crosscutting pegmatite dykes. Analysed ho...

Ar‐Ar ages of hydrothermal muscovites constrain the age of gold mineralisation in the Wiluna greenstone belt, Western Australia. A single muscovite sample from the Matilda M1 deposit, hosted in the greenschist‐amphibolite facies Matilda domain, has a Ar‐Ar plateau‐like segment corresponding to an age of 2623 ± 12 Ma (2 σ). This is interpreted as th...

Sm-Nd ages of pegmatite dikes that crosscut gold-bearing structures in the southern Yilgarn Craton, Western Australia, provide minimum age constraints of 2640 ± 11 Ma, 2628 ± 10 Ma, and 2620 ± 36 Ma for gold mineralization at the Westonia and Nevoria (Yellowdine Terrane) and Scotia (Norseman Terrane) gold deposits, respectively. Similarly, a post g...

This study reports Sm-Nd isotope data for hydrothermal scheelite from the Archean Mount Charlotte gold mine in Kalgoorlie, Western Australia. This paper represents the first results of an ongoing investigation into the Sm-Nd isotope systematics of Archean gold deposits in Western Australia. Previous studies of Nd isotopes in scheelites from Archean...

The 40Ar- 39Ar ages of three hydrothermal muscovite samples associated with auriferous gold stockwork systems at the Mount Charlotte deposit in the Kalgoorlie gold field have a weighted mean of 2602 ± 8 Ma. At the nearby Golden Mile deposit 40Ar- 39Ar ages from two muscovite samples associated with shear-hosted lode gold mineralization have a weigh...

Palaeozoic intrusive rocks of the New England Batholith from the Rockvale district in the southern New England Orogen form three distinct associations: (i) the Carboniferous Rockvale Adamellite, a member of the Hillgrove Suite of deformed S‐type granitoids; (ii) a small I‐type igneous complex on the northwestern margin of the Rockvale Adamellite: s...

The Hillgrove mineral field, in the southern part of the New England Orogen of northeastern New South Wales, Australia, contains numerous mesothermal Au-Sb vein systems. Calc-alkaline (shoshonitic) lamprophyre (CAL) dykes are also associated with mineralisation with dilational lode structures acting as conduits for dyke intrusion, which has occurre...

The Southwest Indian ridge extends from the indian Ocean Triple Junction, to the Bouvet Triple Junction; it has been spreading at very low rates throughout the Cenozoic and today is one of the slowest spreading major ridge on the planet, with a half-rate of only 0.6 to 0.9 cm/yr. Our investigation of the Southwest Indian Ridge started 3 years ago w...

We have made in-situ, high spatial resolution (100 mu m), measurements of relative LREE abundances and Pb-isotope compositions in three well-studied Fe-Mn nodules from the SW Pacific by laser-ablation MC-ICP-MS. Our technique enables rapid determination of both relative LREE abundances (enabling calculation of [La/Sm]N and Ce/Ce*) and the 206Pb-207...

Dome lavas from the 2004 eruption of Mount St. Helens show elevated Li contents in plagioclase phenocrysts at the onset of dome growth in October 2004. These cannot be explained by variations in plagioclase-melt partitioning, but require elevated Li contents in coexisting melt, a fact confi rmed by measurements of Li contents as high as 207 μg/g in...